Method and apparatus for the continuous galvanization of the inner surface of tubes



1961 HANS--JOACH|M BAHMANN 2,970,950

METHOD AND APPARATUS FOR THE CONTINUOUS GALVANIZATION OF THE INNERSURFACE OF TUBES 5 Sheets-Sheet 1 Filed Jan. 15, 1959 8 8 8 2 8 8 2 Q2 5A A 1961 HANS--JOACHIM BAHMANN 2,970,950

METHOD AND APPARATUS'FOR THE CONTINUOUS GALVANIZATION OF THE INNERSURFACE OF TUBES Filed Jan. 15, 1959 3 Sheets-Sheet 2 Feb. 1961HANS--JOACHIM BAHMANN 2,970,950

METHOD AND APPARATUS FOR THE CONTINUOUS GALVANIZATION OF THE INNERSURFACE OF TUBES United States Patenti O METHOD AND APPARATUS FOR THECONTINU- OUS GALVANIZATION OF THE INNER SUR- FACE OF TUBES Hans-JoachimBahmann, Paderhorn, Germany, assignor 1 This invention relates togalvanizing, and more specifically to a method and apparatus for thecontinuous galvanization of the inner surface of tubes.

For galvanizing the inner surface of tubes it has already been proposedto employ anodes arranged coaxially within the tubes while the tubesthemselves serve for accommodating the different treatment liquids,especially the electrolyte, which act successively and which aremaintained in constant motion. Contrary to the galvanizing of the outersurface of tubes, it has hitherto not been possible to employ acontinuous run-through process for galvanizing theinner surface oftubes. This has been hitherto carriedout by using dipping tanks in whichthe tubes are placed, preferably in groups. Apart,

from the fact that this process is complicated and timewasting owing tothe relatively long time the preparation requires, other disadvantagesare that these dipping tanks can only be employed for tubes of limitedlength and that, as a rule, it is not possible to galvanize tubes ofdifferent lengths in one and the same plant. Moreover, in the case ofthese known processes and apparatus, it is extremely difficult, owing tothe danger of the electrolyte becoming weaker, to obtain uniformgalvanizing of the inner surface in the case of tubes of very smallinternal diameter.

The object of the present invention is to devise a method and apparatuswhich enable the carrying out of a continuous galvanization of the innersurface of tubes, even when these have a very small internal diameter,for example down to 3 mm., in a run-through process, but at the sametime avoid the disadvantages inherent in the known methods and apparatusWhile also attaining a considerable improvement from an economical pointof view.

'This object is attained by passing the tubes, which arecathode-connected, continuously one after another through bath tanksfilled with treatment liquids and at the same time feeding them along anaxially arranged stationary anode which they surround, supplyinguninterrupted current to the anode by at least a first and a secondcontact-maker arranged at a distance apart, and,

during the movement of the tubes through the plant in longitudinaldirection, automatically sucking the. treatment liquids of theindividual bath tanks into the interior of the tubes, pressmg ittherethrough and, as soon as the rear end of a tube is free, pumping theliquid back into the respective bath tank by means of stoppers.

fixed on the anode in front of the inlet apertures and following theoutlet apertures provided for the tubes in.

i opened at the same time.

escaping through gaps are provided preferably both in 2 suction andpumping efiects automatically produced by the stoppers during therun-through movement of the tubes, the necessary flushing of the innersurface of the tubes to be treated by the different treatment liquidscontained in the individual bath tanks is ensured, without these liquidsbecoming intermixed.

So as to also ensure that the anode is continually supplied with anodecurrent when fresh tubes are continuously fed, each time a tube isslipped on to the introduction end of the anode, the first contact-makerin the run-through direction is broken and at the same time the secondcontact-maker arranged at a distance from the first contact-maker isclosed, preferably automatically, whereas, as the tube continues to runthrough, the first contact-maker is closed and the second contact-makerThe current feed to the tubes is effected preferably bycathode-connected driving rolls which at the same time effect themovement of the tubes, arranged in substantially horizontal position,over the anode extending along the entire length of the galvanizingplant. The method proposed by the invention can obviously be carried outin such a manner that several rows of tubes are passed simultaneously onanodes arranged preferably side by side and at a distance apart in asubstantially horizontal plane through the bath tanks serving for thepretreatment and finishing treatment as well as the galvanizing.

An arrangement particularly suitable for carrying out the methodaccording to the invention comprises a plurality of bath tanks connectedup in series and filled respectively with treatment liquids for thepretreatment, galvanizing and subsequent treatment of the tubes, atleast one anode connected up with contact-makers and extending throughall the said tanks, piston-like stoppers mounted on said anode one infront of the tube inlet aperture and one following the outlet apertureof each of said tanks, and of a diameter corresponding approximately tothe internal diameter of the tubes to be treated, said stoppers beingarranged at a distance apart exceeding the actual length of itsassociated tanks, and a plurality of rolls serving for transporting andguiding the tubes distributed in the longitudinal direction of theanode. At the same time the tubes are guided preferably only in therun-through region of the electrolyte tank by centering elementsarranged on the anode and acting as insulation in relation to the tubewall, these elements being provided with through-flow passages extendingparallel to the longitudinal axis of the anode. In this manner the tubesare automatically held in the necessary uniform distance from thesurface of the anode, which is absolutely necessary for obtaining auniform metal coating. The suction and pumping effect produced by thestoppers is not hampered by the centering elements owing to theprovision of through-flow passages in these elements. On the other handthe through-flow passages effect an advantageous, continuous thoroughmixing of the treatment liquid, so that a reduction in strength or adissociation of the liquid is avoided.

To ensure a uniform feed of the tubes and a sufliciently reliableguiding, cathode-connected driving rolls front of and followingtheelectrolyte tank, while the supporting of the tubes in the remaininglongitudinal region of the galvanizing plant is effected by idle guiderolls preferably arranged inside the bath tanks. So as to catch thetreatment liquid between the inlet and outlet apertures in the bathtanks the plant is in operation,

collecting troughs are provided in front of the apertures,

from which troughs the treattinuously or periodically. of treatmentliquid is prevented while on the other hand for the passage of the tubeswhen e emopso r p it is ensured that the actually necessary 'liquidlevel'in the tank is maintained. Moreover the constant circulation ofthe treatment liquid prevents it from separating into parts in thetanks.

The fact that both the driving rolls on a roll stand arranged in frontof the electrolyte tank and also those of the set of rolls following theelectrolyte tank are connected to the cathode circuit, ensures that,while a tube running ahead is still gripped by the driving rolls of theset of rolls following the electrolyte bath, the next, following tube isalready switched into the current circuit and consequently subjected toelectrolytic treatment.

The diameter of the anode is chosen so that under all circumstancesthere is a sufficient through-flow of electrolyte between the anode andinner wall of the tube and, a sufiiciently high current density. It hasbeen found that, even in the case of tubes with small internaldiameters, the stoppers coordinated to the bath tanks suffice forsucking the quantity of electrolyte liquid necessary for ensuring asufliciently thick deposition. Even in the case of low runthrough speedsthe filling volume of the tubes increases to such an extent thatsufficient cooling and recuperation of the electrolyte liquid areattained.

The method proposed by the invention covers all types of galvanictreatment, such as zinc plating, copper plating, chroming, nickelplating, polishing and so forth.

The anode is preferably provided along a considerable part of its lengthwith an electric insulating coating which is interrupted by electricityconducting surface sections in the run-through region of theelectrolytetank. A parti ularly practical solution consists in arrangingtubular sections composed of electric insulating and electric conductivematerial fixed in alternating succession on the wireshaped anode in therunthrough region of the electrolyte tank. The electric insulatingtubular sections preferably consist of an elastic moldable plastic proofagainst the electrolyte and are slipped under elastic expansion on totheWire-shaped anode, The electric conductive tubular sectionsconsist ofthe metal to be deposited on the surface of the tubes and have aninternal. diameter corresponding to the external diameter of thewire-shaped anode, so that theycan be slipped on to the anode andrenewed when necessary or can be exchanged for tubular sections composedof another metal, but on the otherv hand are conductively connected withthe outer surface of the anode over their entire inner wall. The lengthofthetubular sections composed. of. electric insulating and electriccon-' ductive materials depends upon the internal diameter of the tubesto be galvanized. and the run-through speedgof;

the tubes. As a rule the total length of the sections oomposed. ofelectric conductive material amounts to only aboutj fit to /2 the totallength of the anode in the region ofthe electrolyte tank,

By the tubular sections composed of the metal to be electrolyticallydeposited on the inner wall of.the tubes and slipped on the anode, it ispossible to effect a continuous regeneration of the electrolyte. thatthe anode within the electrolyte tank is in'contact with the electrolyteonly on a portion of its length through an electricity conductivesurface, the hydrogen formation in the electrolyte is reduced in anadvantageous manner, An intensive formation of hydrogen would,particularly in the case of tubes with small internal diameter, preventuniform galvanizing owing tothe formation of bubbles and liberation ofhydrogen on the cathode-connected inner wall of the tubes.

Between the tubularsections of electric insulating and electricconductive materials arranged on the wire-shaped, anode, centeringelements are provided preferably at uni-' form'distances apart, whichelementsare principallyof cortical shape and are also slipped on to thewire-Shaped anode.

"The stoppers and the centering elements are soconstructed thatthey'insulate thetubewall from theanode T Owing to the fact.

ca'rrbe achieved most simply by'rnaking the stoppers and centeringelements from an electric insulating material, particularly syntheticsubstance.

It is evident that there is no reason why further anodes, for examplezinc plates, should not be additionally arranged within the electrolytetanks outside the tubes, so as to coat also the outer surfaces of thetubes electrolytically with a metal layer.

A'preferred embodiment of the invention is hereinafterdescribed'by wayof example with reference to the accompanying drawings, in which:

Fig. 1 is a longitudinal section through a galvanizing plant;

Fig. 2 is a longitudinal section through an anode provided withcentering means;

Fig. 3 is a cross section taken on lineIII lIIof Fig. 2;

Fig. 4 illustrates a set of driving rolls, and

Fig. 5 shows a contact-maker for the anode current.

Fig. 1 shows steel tubes 1 which have an internal diameter of about '3mm. and are slipped. on a horizontally arranged anode 2.

The anode 2 consists, of. a. copper wire 3 which isencased on aconsiderable part of its length, in an. electric insulating material 4,such as e.g, rubber or plastic. The. anode 2 is stationary, and arrangedaxially, extendingv through bath tanks, 5, 6, 7 and 8 arranged. one,behind the other, Whereas the copper wire 3 outside the tank 7,. whichservesaselectrolyte bath, is providedwiththeelecs' tricinsulatingmaterial 4 along its entire lengthwiththe. exception of sections 3 a and3b, within the electrolyte. tank 7 tubular sections of electricinsulating material 4 andv tubular sections 4a of electric conductivematerial; are slipped on the copper wire 3 of theanodel in alterw natingsuccession as shown in Fig. 2. The tubular sectionsv of the electricinsulating material 4 tightly surrounding the. anode 2 arepreferablymade from plasticwith rubber-,- like characteristics which isnot attacked bytreatment, liquids and especially the electrolyte. Thetubular sec: tions 4g, likewise firmly seated on the copper wire 3, of,the anode 2 consist, in the example illustrated in the drawn ings, ofzinc tubesiwhich are made from a 99.9% ,clectrw, lytic zinc.

Thelevel of the treatment liquids in the bath tanks.5 to. 8 ismaintained, preferably automatically, at a height. which ensurescomplete flooding of the anode 2 and the wheel. On the ranges of lengthdirectly in front of and following the bath tanksS, to8, the anode Zisprovided; with piston-like stoppers 9a and 9b which, in the examplej.illustrated in thedrawings, are made froma rubber-like, electricinsulating plastic which shows no signs of swelling. inthe presence ofoil and acids The stoppers 9a and, 9b are also'firmly seatedon thecopper wire. 3 and their; greatestcross section corresponds to theinternal diameter of the tubes 1 to be treated, so that they beartightly" against the inner wall of the tubes. The stoppers. 9a and9,b"taper like' ja circular cone arranged coaxiallyvto thel anode 2 inthe opposite direction .to the run-through direc-i: tion of the tubeslindicated by arrow x. On the range of length located within theelectrolyte tank 7 the anode is, provided with centering cones 10, thegreatest cross'sec tion ofwhich also correspondsto the internal diameterof thetubes 1. The'centering cones 10 are made from an electricinsulating plastic possessing high wear-resisting, and low deformationproperties, for example from polyvinylchloride, which is also notattacked by the electrolyte. As can beseen from Fig. 2, the centeringcones 10 are arranged between the'tubular sections of the electricinsulating material 4 and the tubular sections 4a mountedon the wire 3of the anode 2. The centering cones haveconcentric radial aperturesconstructed as through; fl'ow passages 10a for the electrolyte andextending pa a -j lel to the axis of the anode, see Fig. 3.Thecente'ring cones- 10. are preferably arranged at about uniform distances apart one behind the other on the copper'wire' 3.

For the current feed, the ;copper wire 3 outside the electrqlyte tank ,7lies exposed merely on the two sections" 3a and 3b at a distance apart,the section 3b being of greater length than the section 3a. The exposedcopper wire sections 3:: and 3b are, as can be seen from Fig. 5, limitedby holding cones ll of insulating material. The length of the exposedcopper wire section 3b is preferably so chosen that tubes of practicallyany lengths coming into question can be galvanized in a continuousoperation.

For feeding anode current two contact-makers 12a and 12b are providedwhich are coordinated to the sections 3a and 3b of the copper wire 3which are not insulated. The contact-makers 12a and 12b are providedwith a slot open in upward direction and of a width correspondingsubstantially to the diameter of the copper wire 3, and are arranged ina roller bed 13 so that they can be lowered in such a'manner thatuninterrupted current is always fed to the copper wire 3 of the anode 2by one of the two contact-makers 12a and 12b. Thereby the alternatingcontact-making can be regulated for example photo-electrically inaccordance with the position of a tube to be treated or by a mechanicalfeeling device. To adapt the spacing of the contact makers 12a and 12bto an actual tube length, the contact-maker 12b is, in the exampleillustrated in Fig. 1, arranged to slide to and fro in the run-throughdirection indicated by the arrow x. For this purpose the contact-maker12b can be mounted longitudinally shiftable within the roller bed 13parallel to the anode 2. But it is also possible to build the roller bed13 itself in such a manner that the part of the roller bed carrying thecontact-maker 12b can be shifted to and fro in the run-throughdirection.

The roller bed 13 is provided with a plurality of transport rollers 14arranged below and transversely to the anode 2 and which run freely. Itis, however, also possible to construct the rollers 14 so that at leastsome of them can be mechanically driven. The rollers 14 are arrangedwith their periphery at such distance from the anode 2 that the tubes Islipped on to the anode 2 can be moved on the transport rollers 14substantially coaxially to the anode in the run-through directionindicated by the arrow x. For this purpose the rollers are preferablyprovided with a groove conforming approximately to the external diameterof the tubes 1.

Roll stands 15 and 16 arranged respectively in front of and followingthe electrolyte bath 7 each comprise two driving rolls 15a, 15b and 16a,16b respectively which are driven at the same speed and connected to thecathode circuit. The driving rolls 15a, 15b and 16a, 16b respec- Vtively are each adjustable in a vertical plane extending in therun-through direction in such a manner that their relative'spacing canbe adapted to the different external diameters of the tubes to betreated. Each of the driving rolls 15a, 15b and 16a, 16b respectively isprovided with a groove 15c and 16c, which corresponds approximately tothe external peripheryof the tubes to be treated, see Fig. 4. Aparticularly practical form of construction for the roll standscomprises two cathode-connected rolls, provided for supporting the tubesto be treated and arranged one behind the other at a distance apart,whereas a roll engaging the tubes from above and arranged in the lengthsection located between the two lower rolls is constructed as drivingroll. The driving roll can for this purpose be provided with a groove ofplastic with transverse ribs.

The tank 7 contains electrolyte liquid 17 which, in the exampleillustrated in the drawings, consists primarily of a zinc sulphatesolution. The level of the electrolyte liquid 17 is slightly above atube inlet aperture 18a provided on the front end of the tank 7 and atube outlet aperture 18b provided on the rear end of the tank 7. Theapertures 18a and 18b can with advantage by provided on theircircumference with packing sleeves of flexible material to offer acertain amount of resistance to the flowing out of the electrolyteliquid. Below the tube inlet aperture 18a and the tube outlet aperture18b collecting troughs 19a and 19b respectively are provided forcatching the electrolyte escaping through the end apertures in the tank.For pumping back the electrolyte liquid which is caught in thecollecting troughs 19a and 19b a pump (not shown in the drawings) iscoordinated to the tank 7 so that a continuous circulation ofelectrolyte liquid and the maintenance of the necessary level oftreatment liquid are ensured. In addition, a circulating pump (also notshown in the drawings) is provided for preventing impoverishment inmetal, which would detrimentally affect the uniform separation and alsoheating of the electrolyte liquid to an excessive extent. Loose guiderollers 20 are provided in the tank 7 for supporting and guiding thetubes.

The bath tanks 5 and 6 connected up in front of the electrolyte tank 7as well as the bath tank 8 connected up behind it are of substantiallythe same construction as the tank 7. Each of these tanks is alsoprovided with a tube inlet aperture 18a on its front side and a tubeoutlet aperture 18b on its rear side and the anode 2 passessubstantially coaxially through these apertures. Collecting troughs 19aand 19b are also arranged on the front and rear sides respectively ofthese tanks for catching treatment liquid escaping from the particulartank. The tanks 5, 6 and 8 arranged in front of and following theelectrolyte tank 7 contain guide rollers 2G for supporting and guidingthe tubes 1.

The bath tank 5 is filled with a degreasing liquid 21, whereas the tank6 in front of the tank 7 contains a flushing liquid 22. The last bathtank 8 also contains a flushing liquid 23. In addition a pump is alsocoordinated to each of the tanks 5, 6 and 8 arranged in front of andfollowing the electrolyte tank 7 for pumping back the treatment liquidcaught in the collecting troughs 19a and 19b, and also a circulatingpump for continuously circulating the treatment liquid. The pumps arealso in this case not shown in the drawings for the sake of clearness.The level of the treatment liquids contained in the bath tanks 5, 6 and8 is also slightly higher than the tube inlet and outlet apertures 18aand 18b of these tanks.

Another roller bed 24 with transportrollers 25 is connected up behindthe galvanizing plant, the transport rollers 25 of this bed arrangedtransversely to the runthrough direction being all freely rotatable orin part capable of being mechanically driven.

The method of operation is as follows:

After the current contact-makers 12a and 12b have been set at a distanceapart which is slightly greater than the length of the tubes to betreated, the tubes 1 are slipped one after the other on to the anode 2in the direction of the arrow x. As the tubes are slipped on,

the anode 2 receives current via the contact-maker 12b, whereas thecontact-maker 12a is broken. When the rear end of a tube releases thecontact-maker 12a, this closes the circuit whereas at the same time thesecond contact-maker 12b in the run-through direction indicated by thearrow x opens or breaks. The tube 1 can then be transported withouthindrance in the run-through direction and is moved on by the transportrollers 14 in the direction of the arrow x. During this movement, thetube is pushed over the stoppers 9a arranged in front of the bath tank 5and its front end subsequently enters the tube inlet aperture 18a in thetank 5. Seeing that the front tube opening is surrounded by thedegreasing liquid 21 in the tank 5, a suction effect is caused by thefront stopper 9a as the tube moves forward, so that the inner surface ofthe tube 1 is now flushed by the degreasing liquid 21 and degreased.This suction effect is maintained until the front end of the tubereaches the stopper 9b following the tank 5, by which stopper thedegreasing liquid sucked into the tube and located between the twostoppers 9a and 9b coordinated to the bath tank 5, is forced through thetube until the rear end of the tube is free of the front stopper 9a,wherebath tanks.

upon the degreasing liquid is pumped back through the ear end of thetube into the bath tank S by the stop- Subsequently the front opening ofthe tube is pushed over the-frontstopper 9a of thenext-followingflushing tank 6, if necessary with the "aid of 'an'intermediary driving roller set. Inside this tankthe manner of operationis the same as that in the tank 5, that is the flush ing liquid 22 inthe tank 6 is sucked into the interior of the tube until the front endof the tube reaches" the stopper 9b behind the tank 6,'when, on the rearend of the tube becoming free, the flushing liquid is pumped back intothe bath tank 6 by the stopper 9b.

The tube pretreated in this manner is now' gripped by the driving rolls15a, 15b of the roll stand 15. Thereby, after the tube has beenslippedover'the stop- :per 9a arranged in front of the electrolyte tank7 and introduced through the tube'inlet aperture 18a into' theyelectrolyte liquid, the circuit is closed so that the galvanization ofthe inner surface of the tube can start up. Hereby the tube'is fedthrough the plant at'a runthrough speed which is dependent on the onehand upon :thethickness of the metal coating it is desired to ob tainand on the other hand upon the concentration of the electrolyte and thedensity ofthe current employed.

' v The tube travels during its run-through movernent through theelectrolyte tank 7 over thecentering cones of the anode 2 so that auniform coating of the metal deposit is obtained on the inner surface ofthe tube. The electrolyte liquid sucked into'the tube by the stopper 19ais drawn in through the passages 10:; inthe centering H cones 10 untilthe front end of the tube'reaches the stopper 9b at the outlet aperture18b of the electrolyte tank 7, by which stopper the electrolyte liquidis pressed towards the rear through the passages 10a in the centeringcones 10 and, when the rear end of the tube becomes free, out of thetube; The tube is subsequently gripped by the driving rolls 16a and 16bof the roll'stand 16,

which rolls keep the tube connected up in the current circuit. In themeantime the 'next fol'owing tube is simultaneously connected u'pin thecircuit by the roll stand arranged in front of the electrolyte tank 7and sub jected to electrolytic treatment. The driving r'ollslGa and 16bof the roll stand 16 in the meantime guide the preceding tube to theflushing tank 8 in which the flush- "ing, liquid 23 is first sucked intothe interior ofthe tube and subsequently pumped out of the tubesagain bythe stoppers 9a and9b. i

When the galvanizing plant is no longer in use, bottom valves on theindividual bath tanks are opened and the treatment liquids flowing outtherefrom are cau ht in the collecting troughs coordinated to theindividual The invention may be embodied in other specific forms withoutdeparting from the'spirit or essential characthe bath tanks a tube isfree, pumping 8 the liquid back into the respective bath tank. '1

2, Method as .setforth--in claim- 1, wherein several rowsof tubes arefed simultaneously on a corresponding'nurnber o f anodes arranged in ahorizontal plane preferably side by side and at a distance apart through'3; Apparatus for electroplating the inner surface of tubes havinginternal diameters down to 3 mm. and impermeable walls in a continuousoperation, comprising a plurality of bath tanks connected up in seriesand adapted to be filled respectively with treatment liquids for thepre-treatment, electroplating and subsequent treatment of the tubes,each of said tanks having a tube inlet aperture and a tube outletaperture at least -one anode connected up with contact-makers andextending throughsaid aperture of said tanks, a plurality of vpiston-like stoppers mounted on said anode one in front ofdthe tubeinlet'apertureand one following the outlet aperture of each of saidtanks, and of a diameter corresponding approximately to the internaldiameter of the n tubes to betreated, said stoppers'being'arranged at a-distance apart exceeding the actual'length of its assoelated tanks, anda plurality of rolls serving for transporting and guiding the tubesdistributed in the'longitudinal directionof the anode.

4. Apparatus as set forth in claim 3, wherein centering elements forguiding the tubes are arranged on the v anode preferably only inthe'run-through regionof that trolytetank, and loosely mounted guiderollers are arranged preferably inside'the tanks for supporting thetubes on the remaining portion of the length of the galvanizing plant.

I 6. Apparatusasset forth in claim 3, wherein the anode is provided withan electric insulating coating on a considerable portion of its length.7 1

7; Apparatus as set forth in claim 3, wherein the-anode is provided withan electric insulating coating on a considerable p ortionof'its length,said insulating coating being interrupted by electric conductingsurfacesections in the runthrough region of the electrolyte tank. v

s8.;Ap-paratus asset forth in claim 3, wherein the anode H is in'theform of a wire and is coated with alternating teristics thereof. Thepresent embodiment is therefore 7 to be considered in all respects asillustrative and'not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come Within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

, Iclairn:

'1. Method of electroplating in continuous operation the inner surfaceof tubes having impermeable walls and internal diameters down to 3 mm.,comprising the steps tubular sections composed respectively of electricinsulating material and electric conductive material.

9. Apparatus as set'forth'in claim 8, wherein centering cones for thetubes are'arranged on the wire anode between the tubular sectionspreferably at uniform distances apart. 1 I

10." Apparatus as set forth in claim 3,wherein the pistonlike stoppersand centering elements for the tubes are made 'of electric insulatingmaterial of the group consisting "of plastics. I '11. Apparatus'assetforth in claim 10, wherein the '1 stoppers'andthe centering elementstaper in conical shape awa'y"frorri the'run through direction, thecentering elements having a plurality of apertures forming "flowofpassing cathode-connected tubes continuously one after ranged stationaryanode which they surround, supply- ;ing uninterrupted current to theanode during the movement of the tubes through the plant in longitudinaldi'- I rection, automatically sucking the treatment liquids of 1 1 theindividual bath tanks into the interior of the tubes, pressing ittherethrough and, as soon as the rear end of I another through bathtanks filled with treatment liquids and at the same time feeding themalong an axially ar- 5-1.

through passages distributed around its peripheryandextendingparallelfto the axis of the anode.

12:? Apparatus as set forth in claim 3', wherein.at ileast -oneof thecontact rnakers is adjustable in the run-through clire ctioriof thetubes. 4

1 3. Apparat s a s set fo rthclaim '3, whereincollecting troughs arearranged under the tube outlet and tube inlet aperturesof each tankforcatchin g treatment liquids escaping through the inlet and outletapertures.

one pump is coordinated to each bath tank tor pumping the treatmentliquid out of a collecting trough back into its tank.

15. Apparatus as set forth in claim 3, wherein several anodes arrangedapproximately parallel to each other and side by side at a distanceapart are coordinated to each of the bath tanks arranged one behind theother in a substantially horizontal plane.

16. Apparatus for electroplating the inner surface of metal tubes havingimpermeable walls in a continuous operation comprising, in combination,a tank having a pair of opposite walls being each formed with anaperture therethrough aligned with each other and having a preselecteddiameter substantially equal to the diameter of the tubes to beelectroplated, said tank being adapted to be filled with electrolyte;combined anode and pumping means extending through said apertures forsucking electrolyte from said tank into the interior of a tube movingthrough one of said apertures into said tank and for pushing theelectrolyte out of the interior of the tube as the tube leaves said tankthrough the other of said apertures and for connecting the electrolytein the tube to one pole of an electric current supply during themovement of the tube through the tank; and combined moving and cathodemeans for moving a plurality of tubes successively through saidapertures of said tank and for connecting the tubes during theirmovement thereof through said tank to the other pole of the currentsupply, whereby the interior of said tubes will be electroplated as thetubes move through said tank.

17. Apparatus for electroplating the inner surface of metal tubes havingimpermeable walls in a continuous operation comprising, in combination,a tank having a pair of opposite walls being each formed with an aperi14. Apparatus as set forth in claim 3, wherein at least" turetherethrough aligned with each other and having a preselected diametersubstantially equal to the diameter of the tubes to be electroplated,said tank being adapted to be filled with electrolyte; combined anodeand pumping means extending through said apertures for suckingelectrolyte from said tank into the interior of a tube moving throughone of said apertures into said tank and for pushing the electrolyte outof the interior of the tube as the tube leaves said tank through theother of said apertures and for connecting the electrolyte in the tubeto one pole of an electric current supply during the movement of thetube through the tank; means in said tank for supporting the tubesduring their movement therethrough aligned with said apertures; meansmounted on said combined pumping and anode means for supporting the samein the interior of the tubes moving through the tank coaxial with thetubes; and combined moving and cathode means for moving a plurality oftubes successively through said apertures of said tank and forconnecting the tubes during the movement thereof through said tank tothe other pole of the current supply, whereby the interior of said tubeswill be electroplated as the tubes move through said tank.

References Cited in the file of this patent UNITED STATES PATENTS938,489 James Nov. 2, 1909 947,440 Greenfield Jan. 25, 1910 1,733,404Fahrenwald Oct. 29, 1929 1,927,162 Fiedler et al Sept. 19, 19331,956,722 Kennedy May 1, 1934 1,997,013 Potthofi Apr. 9, 1935 2,019,709Kennedy Nov. 5, 1935 2,100,587 Chalker Nov. 30, 1937 2,408,358 Curtis eta1 Aug. 30, 1949 2,859,157 Curtiss Nov. 4, 1958

1. METHOD OF ELECTROPLATING IN CONTINUOUS OPERATION THE INNER SURFACR OFTUBES HAVING IMPERMEABLE WALLS AND INTERNAL DIAMETERS DOWN TO 3 MM.,COMPRISING THE STEPS OF PASSING CATHODE-CONNECTED TUBES CONTINUOUSLYONLY AFTER ANOTHER THROUGH BATH TANKS FILLED WITH TREATMENT LIQUIDS ANDAT THE SAME TIME FEEDING THEM ALONG AN AXIALLY ARRANGED STATIONARY ANODEWHICH THEY SURROUND, SUPPLYING UNINTERRUPTED CURRENT TO THE ANODE DURINGTHE MOVEMENT OF THE TUBES THROUGH THE PLANT IN LOGITUDINAL DIRECTION,AUTOMATICALLY SUCKING THE TREATMENT LIQUIDS OF THE INDIVIDUAL BATH TANKSINTO THE INTERIOR OF THE TUBES, PRESSING IT THERETHROUGH AND, AS SOON ASTHE REAR END OF A TUBE IS FREE, PUMPING THE LIQUID BACK INTO THERESPECTIVE BATH TANK.